Validation of Transabdominal Fetal Pulse Oximetry in Hypoxic Fetal Lamb Models

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Project Summary Despite significant cost and clear evidence of health risks associated with Cesarean deliveries (C-sections), an unnecessarily large number of infants are delivered via C-sections in the US. The high rate of C-sections in the nation, relative to globally accepted norms, is in part attributed to the high false positive rate of fetal distress, associated with the current half-a-century-old intrapartum fetal monitoring technology. The long-term vision of this project is to alleviate this problem, by developing an improved and more specific technology for intrapartum fetal health monitoring. Specifically, we have developed the technology and built a device prototype for non-invasive, transabdominal measurement of fetal arterial blood oxygen saturation (FSpO2). The device works by shining light in the abdominal area at two specific near infrared wavelengths, followed by sensing the weak back scattered light reflections transcutaneously. The sensed signals are subsequently processed to remove various noises, including the unwanted maternal contributions, from the measurements to infer variations in light intensity that are strictly due to pulsation of fetal arteries. The device prototype is successfully validated in several preliminary tests, including simulations, photo-plethysmography (PPG) acquisition in human subjects through a thick optical phantom mimicking optical properties of a pregnant woman's abdominal area, PPG detection and separation of emulated fetal signal through an emulated maternal tissue, and in-vivo validation in a hypoxic fetal lamb model. To further advance the technology, we aim to investigate device's accuracy and reliability in measuring FSpO2 in hypoxic fetal lamb models (n=18). Our animal study protocol, already demonstrated to be effective in our preliminary work, includes hysterotomy to cannulate lamb fetus for fetal hemodynamic monitoring and drawing fetal blood samples, and placement of an inflatable catheter in the maternal aorta through which, we regulate the ewe's blood supply to the uterus, and induce controllable fetal hypoxia. The study will enable us to collect gold standard fetal arterial blood oxygen saturation (FSaO2) data via arterial blood gas (ABG) tests, under a number of hypoxia scenarios, and to compare them against our device's concurrent measurements. The study is organized into two complementary groups, depending on whether the uterus is closed around the fetal neck (n=9) or the fetus is fully returned to the uterus (n=9) before closing ewe's abdominal fascia, which enables us to isolate the impact of different tissue layers, and to characterize the technology's operating range and limitations. The project will provide the foundation for unleashing the potential clinical impact of the technology down the road.